A nuclear fuel assembly for Pressurised Water Reactor, “PWR”, generally comprises of a bundle of nuclear fuel rods of great length arranged parallel to each other and a frame for holding the rods comprising of a bottom tie plate, a top tie plate, guide tubes being substituted for certain rods of the bundle and interconnecting between them the bottom tie plate and the top tie plate, and spacer grids attached to the guide tubes and distributed between the bottom tie plate and the top tie plate. The rods are held transversely and longitudinally by the spacer grids.
The nuclear fuel assembly has an elongated shape and its length is of the order of several meters, typically about four meters long, with a mass of several hundred kilogrammes, typically of the order of 600 to 800 kg. As a result, operations of handling nuclear fuel assemblies are often difficult.
In light of its use, the nuclear fuel assembly is arranged vertically in a nuclear reactor core, with the bottom tie plate being disposed at the bottom and top tie plate at the top.
During operation, it is possible that one of the fuel rods of the nuclear fuel assembly or the holding frame may be damaged and must be replaced. In addition, the fuel rods are regularly extracted for the purposes of carrying out laboratory examination or for reintegration into the bundle of rods of another fuel assembly for experimental purposes.
Nuclear fuel assemblies are generally designed so as to be able to extract each rod from the frame after the dismantling of one of the tie plates. In general, the extraction of the rod is carried out from the top after the dismantling of the top tie plate. In some cases, for example in the event of breakage of a fuel rod and when the two pieces have to be extracted or when all of the fuel rods must be transferred from a damaged frame to a new frame, it may be necessary to carry out the extraction from the bottom of the assembly after dismantling of the bottom tie plate. In this case, it is necessary to first turn over the nuclear fuel assembly. All these operations are carried out under water in order to avoid exposure to radiation.
FR 2 666 680 discloses a turning assembly comprising of a nuclear fuel assembly container, also called “cell”, and a device for turning the container. The container comprises two coaxial trunnions provided on two opposite faces of the container. The turning device comprises of a lifting beam capable of being suspended from a crane, the lifting beam consisting of two columns that are spaced apart in a manner so as to receive between them the container, and two bearing members positioned at the lower ends of the columns and capable of being used for bearing on the trunnions of the container while enabling the rotation of the container about a horizontal turning axis, the turning device further comprising of a drive arm mounted on the lifting beam so as to be rotatable around the turning axis in order to drive the container, supported on the supporting members, in rotation about the turning axis.
However, this turning assembly requires the use of a crane for suspending the lifting beam. The crane is thus monopolised and is no longer available to perform other operations, for example the operations of loading/unloading of nuclear fuel assemblies in the reactor core.
Moreover the turning operations using the lifting beam suspended from the crane are carried out in a maintenance pool over the cells for temporary storage of nuclear fuel assemblies. These cells must therefore be emptied for safety reasons, this necessitates the moving of nuclear fuel assemblies to be undertaken, which is very time intensive, before being able to turn over the nuclear fuel assembly on which repairs and/or replacement of fuel rods and/or of the support frame must be carried out.